3,507 research outputs found
On the Necessity of Rational Velocities: a Gedankenexperiment
In the present contribution we propose a gedankenexperiment in which the
restriction of rational values on the velocities emerges as a necessary
condition from Classical Electromagnetism and Quantum Mechanics. This
restriction is shown to be intimately connected to Dirac's electric charge
quantization condition.Comment: 4 pages IFUSP/P-105
N-loop Treatment of Overlapping Diagrams by the Implicit Regularization Technique
We show how the Implicit Regularization Technique (IRT) can be used for the
perturbative renormalization of a simple field theoretical model, generally
used as a test theory for new techniques. While IRT has been applied
successfully in many problems involving symmetry breaking anomalies and
nonabelian gauge groups, all at one loop level, this is the first attempt to a
generalization of the technique for perturbative renormalization. We show that
the overlapping divergent loops can be given a completely algebraic treatment.
We display the connection between renormalization and counterterms in the
Lagrangian. The algebraic advantages make IRT worth studying for perturbative
renormalization of gauge theories.Comment: 12 figures eps, 61 pages, final versio
Preparation of Schr\"{o}dinger cat states of a cavity field via coupling to a superconducting charge qubit
We extend the approach of Ref. [Yu-xi Liu, L. F. Wei, and F. Nori, Europhys.
Lett. 67, 941 (2004)] for preparing superposition states of a cavity field
interacting with a superconducting charge qubit. We study effects of the
nonlinearity on the creation of such states. We show that the main contribution
of nonlinear effects is to shorten the time necessary to build the
superposition.Comment: arXiv admin note: text overlap with arXiv:1301.609
Stochastic coupling in two modes systems: the weak-strong coupling transition
We investigate the weak-strong coupling transition of two linearly coupled
systems under the influence of a phase fluctuating coupling. In the weak
coupling regime the exponential decay of quantum properties is well known. A
different scenario occurs in the strong coupling regime, the inhibition of the
dynamics which tends to "freeze" as the ration between coupling strength and
average phase fluctuation time increase. Exciton-polariton oscillations and the
self-trapping phenomenon in Bose-Einstein Condensate qualitatively illustrate
the weak and strong regimes respectively
Towards the understanding of Decoherence on Ion Traps
Two mechanisms of decoherence in ion traps are studied, specially related to
the experiment [Kielpinski et al., Science 291 (2001) 1013]. Statistical
hypothesis are made about the unknown variables and the expected behaviour of
the visibility of the best experimental pattern is calculated for each
mechanism. Data from the experiment are analyzed and show to be insufficient to
distinguish between them. We suggest improvements which can do this with slight
modifications in the present facilities.Comment: 7 pages, 4 figures, submitted to Phys Lett
Axial Monopoles, The Quantization of Electric Charge and a Dynamical Discreteness of Space-Time
In the present contribution we show that the introduction of a conserved
axial current in electrodynamics can explain the quantization of electric
charge, preserving parity conservation, and introduces a dynamical discreteness
into space-time.Comment: 9 page
Axial Currents in Electrodynamics P.C.R
In the present work we argue that the usual assumption that magnetic currents
possess the vector structure characteristic of electric currents may be the
source of several difficulties in the theory of magnetic monopoles. We propose
an {\it axial} magnetic current instead and show that such difficulties are
solved. Charge quantization is shown to be intimately connected with results of
theories of discrete space time.Comment: 9 pages IFUSP/P-105
Aspects of the competition between atom-field and field-environment couplings under the influence of an external source in dispersive Jaynes-Cummings model
We give a fully description of the dynamics of an atom dispersively coupled
to a field mode in a dissipative environment fed by an external source. The
competition between the unitary atom-field (which leads to entanglement) and
the dissipative field-environment couplings are investigated in detail. We find
the time evolution of the global atom-field system for any initial state and we
show that atom-field steady state is at most classically correlated. For an
initial state chosen, we evaluate the purity loss of the global system and of
atomic and field subsystems as a function of time. We find that the source will
tend to compensate for the dissipation of the field intensity and to accelerate
decoherence of the global and atomic states. Moreover, we show that the degree
of entanglement of the atom-field state, for the particular initial state
chosen, can be completely quantified by concurrence. Analytical expression for
time evolution of the concurrence is given.Comment: 19 pages, revtex4, 3 figure
Universality of finite time disentanglement
In this paper we investigate how common is the phenomenon of Finite Time
Disentanglement (FTD) with respect to the set of quantum dynamics of bipartite
quantum states with finite dimensional Hilbert spaces. Considering a quantum
dynamics from a general sense, as just a continuous family of Completely
Positive Trace Preserving maps (parametrized by the time variable) acting on
the space of the bipartite systems, we conjecture that FTD happens for all
dynamics but those when all maps of the family are induced by local unitary
operations. We prove this conjecture valid for two important cases: i) when all
maps are induced by unitaries; ii) for pairs of qubits, when all maps are
unital. Moreover, we prove some general results about unitaries/CPTP maps
preserving product/pure statesComment: 7 pages and 2 figures. New title. Improved version! Comments are
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Multipartite entanglement control via Quantum Zeno Effect
We develop a protocol based on 2M pairwise interacting qubits, which through
Quantum Zeno Effect controls the entanglement distribution of the system. We
also show that if the coupling constants are different the QZE may be used to
achieve perfect entanglement swap
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